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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // 用户输入年份，输出当前年份2月的天数
        function backDay(){

            let year =prompt('请输入年份');
            let flasg =isLeapYear(year);
            if(flag){
                console.log(year + '年的2月份有29天');
            }else {
                console.log(year + '年是平年，2月份有28天');
            }
        }

        // 判断闰年的函数
        function isLeapYear(year){
            let result =false;
            if((year %4 ==0)&& (year % 100!=0)|| (year % 100 == 0 && year % 400 == 0)){
          return result;
            }
        }
    </script>
</body>
</html>